1. Field of the Invention
The invention relates in general to electronic reproduction technology for multicolor printing processes and apparatus and particularly to the production of color pictures and proofs for quality control before actual printing occurs.
2. Description of the Prior Art
In electronic reproduction of color masters three primary measured color value signals are obtained in a color scanner by means of point-to-point and line-by-line trichromatic master scanning and opto-electronic conversion of the scanning light with the three primary measured color value signals being a measure of the color components of red, green and blue of the scanned image points. A color correction computer corrects the measured color value signals and in the case of four color printing generates four color separation signals for preparation of color separations of "yellow", "magenta", "cyan" and "black". The color separation signals determine the amounts of yellow, magenta, cyan and black which will be printed with the printing ink during printing.
The printing forms for printing are then produced from the color corrected color separation signals.
Printing occurs by superimposed printing of the printing forms which are inked with the four different color printing inks on a single sheet of paper with a printing machine for the associated printing method.
So as to monitor the anticipated printing results, particularly the color before the actual circulation run or press run occurs and also if desired to make further corrections of the printing forms, proofs are produced from the printing forms with special proofing machines before the press run occurs. Such proofs thus can only be produced when the printing forms already exist.
Color checking methods in which the color controlled images can be produced in a photographic manner allow monitoring possibilities for the final production in the reproduction process which is to later occur and before the manufacture of the printing form. Also, the color separations make it possible for one skilled in the art to draw conclusions concerning the color impressions of the final product and of correspondingly correcting the color separations. These possibilities of supervising and adjusting the colors however are eliminated in modern reproduction equipment and systems, since the production of the color separations on film material eliminated as an intermediate step prior to the printing form and a purely data-wise processing of a master up to the printing form occurs instead.
Monitors which are color display devices wherein the results of the multicolor print is simulated on a color monitor can also be employed for color monitoring before the production of the printing forms. Printing simulation computers are available for print simulation in which the color separation signals are converted into drive signals for the color monitor and which consider the printing parameters and the properties of the color monitor such that the screen picture gives the same chromatic impression as does the anticipated multicolor print on the single edition paper. Print simulation on a color monitor has the disadvantage that only a transient image occurs which is when the image is projected on the monitor.
In the printing industry, however, it is desired to have a physical colored control images so-called proofs available which can be sent to the customer for evaluation for his authorization of the printing order.
For these proofs to provide a reliable color indication concerning the reproduction quality of the multicolor print which is to be later produced they must coincide colorimetrically with the highest possible degree with the actual multicolor print which is to be produced.
A recording device has been disclosed in International Patent Application No. PCT/AU 80/00006 (WO 80/02467) wherein color films are exposed by chromatic laser light which is modulated by stored image data. This known recording device, however, is not suitable for producing proofs in multicolor printing because this apparatus does not specify how the color separation signals must be converted into corresponding modulation signals for the laser light so that the multicolor print and proof are isochromatic.
This invention concerns the production of monochrome or color images on photographic film from data provided by digital computer. Although such data may take any form, the present invention is particularly suited to producing detail color composite images of land terrain from digital spectral data provided by LANDSAT and NOAA satellites.
The principle object of the present invention is to provide a laser-base system for producing images on film using data from a computer which will overcome or avoid the inherent problems of stability and/or alignment of the light beam or beams. With such a system, the advantages of the high-intensity laser output can be realized in more rapid scanning of the beam over the film, or improved picture quality, or both. In regard to multicolor image systems, the present invention provides an arrangement which will allow beams from different lasers to be combined together and brought to a focus simultaneously at one spot on the film (or other image producing medium) so that further advantages of speed are realized without sacrificing fidelity.
This invention concerns the production of monochrome or colour images on photographic film from data provided by a digital computer. Although such images may take any form, the present invention is particularly suited to producing detailed colour composite images of land terrain from digital spectral data provided by LANDSAT and NOAA satellites.
Referring now to FIG. 6, the apparatus illustrated is a three-colour system employing three lasers as light sources. The laser 110 is a helium-cadmium laser having an output of 10 milliwatts at a wavelength of 0.442 micrometers. Laser 111 is a 50 milliwatt argon ion laser having an output wavelength of 0.5145 micrometers. Laser 112 is a helium neon laser having an output of 5 milliwatts at a wavelength of 0.6328 micrometers. High quality lasers with good long term output stability and minimal high frequency (MHz) fluctuations are most desirable for the system. Typical lasers are those provided by Spectra-physics International, Model No. 120 (helium/neon) and Model No. 122-03/262 (argon), and the Linconix laser Model No. 4110 (helium cadmium).
As shown in FIG. 6, a portion of the output of each laser is sampled by the use of a respective pellilcle beam splitter 113, 114 or 115. The sampled portions of the laser beams are directed on to the respective photo-diodes 116, 117 and 118, the outputs of which are compared with reference voltages 133, 134, 135 established during the initial calibration of the equipment. The differences between the photo-diode outputs and the reference voltages are amplified and input to the power supplies 136, 137, 138 of the electro-optical modulators 119, 120, and 121.
The main portions of the laser beams are passed through respective electro-optical modulators 119, 120 and 121. Each of these modulators is controlled by a drive circuit 126, which is in turn controlled by an interface network which is fed with digital electronic information from an electronic computer (not shown). The three analogue voltage outputs from drive circuit 126 are connected to the power supplies 136, 137 and 138 of the electro-optical modulators 119, 120 and 121. These signals are the major controlling signals of the modulators. The analogue voltages from the photo diode/reference voltage combinations exercise a "fine-tuning" control of the transmittance of their respective modulators.
The modulated red beam which emerges from modulator 121 is directed via a front surface mirror 122 through a red transmitting dichroic filter 123, and is then reflected from a blue transmitting dichroic filter 124.
The modulated green beam which emerges from modulator 120 is reflected from the red transmitting dichroic filter 123. The laser 111 and its associated modulator 120 are positioned so that on reflection from filter 123, the green beam is aligned to combine with the red beam from mirror 122. The green component of this combined beam is also reflected from the blue transmitting dichroic filter 124.
The modulated blue beam which emerges from modulator 119 is transmitted through the blue transmitting filter 124. Laser 110 and its associated modulator 119 are positioned so that the blue beam is aligned to combine with the red/green beam which has been reflected by filter 124 to produce a combined red/green/blue beam.
This combined red/green/blue beam is then passed through an electro-optical modulator 125 which is adapted to provide chopping of the combined red/green/blue beams. The chopping action of modulator 25 is controlled by its associated power supply 132, which receives signals from the drive circuit 124 to synchronise with the timing requirements of the film recording device.
A color picture recorder with laser exposure for recording video transmissions is disclosed in the periodical Laser+Elektronik-Optik, No. 2/1973. This device cannot be employed in multicolor printing since NTSC color television signals are converted there into modulation signals for the laser light.